I went online and found out a lot of information about boiling water. If you cover the tin and allow the water and air to cool down, the air will cool and contract, lowering the pressure in the tin. If it lowers enough, the partial vacuum will collapse the walls of the can! The boiling point definitely reduces with air pressure. There is a famous demonstration where boiling water or coffee is drunk, the trick is it was in a vacuum chamber where it boiled at room temperature. The actual definition of the boiling point of water is the temperature when the vapor pressure of the water equals the atmospheric